I was having a similar problem when trying to change default svg icon color. For those who are experiencing the similar issue, make sure you check the angular-material version you're currently using. Currently, I'm using the angular-material "0.7.1" and this is quietly important.
NOTE: with my current Angular-material (0.7.1) version, the <mdIcon></mdIcon>
directive only checks to see if attr.Icon is defined or not during postLinking compileFunction. With this implementation, in order to reference your svg icon files, you simply add icon attribute to your <mdIcon icon="iconsDir/path_to_icon_file.svg"></mdIcon>
element directive. Notice in the earlier angular-material version, you might have use md-src-svg for referencing your svg files, its no longer the case in 0.7.1 version.
So if you were using 0.7.1 and following above instruction, you should have your svg icon rendering correctly, now its time to change the background-color of the svg you're using.
Raw svg file before any modification:
<svg version="1.1" xmlns="http://www.w3.org/2000/svg" x="0px" y="0px" width="24px"
height="24px" viewBox="0 0 24 24">
<g>
<path d="M6,2C4.9,2,4,2.9,4,4l0,16c0,1.1,0.9,2,2,2h12c1.1,0,2-0.9,2-2V8l-6-6H6z M13,9V3.5L18.5,9H13z" />
</g>
You should have a folder within your project where you save all your svg icons, in my case, I have a folder named icons where I store all my svg icons. The example svg file above is the non-modified svg icon where I got it from https://github.com/google/material-design-icons. (Default its rendering as a black svg file)
To change the default svg file, you would simple add a fill attribute to your raw svg file. See modified svg file version:
<path d="M6,2C4.9,2,4,2.9,4,4l0,16c0,1.1,0.9,2,2,2h12c1.1,0,2-0.9,2-2V8l-6-6H6z M13,9V3.5L18.5,9H13z" fill="green" />
I simply added fill="green" the path element svg file, and now my svg icon is rendering as color green instead of default black. I know some of you guys might be using a different version of angular-material, but the mechanism of changing default svg color should apply the same. Hopefully this can be helpful to solve your problems, thanks!